Measurements of total chromium and hexavalent chromium have been obtained i
n a laminar methane/air diffusion flame. Chlorine was added to methane in t
he form of methyl chloride gas. A dilution-quenching probe sampled the emis
sions from the flame. Particles were collected on a filter and vapor phase
species were collected in impingers. All samples were analyzed for hexavale
nt chromium with a spectrophotometric method. The filter sample was also an
alyzed for total chromium by X-ray fluorescence. Total chromium added to th
e flame was determined by gravimetric analysis of the chromium source, chro
mium hexacarbonyl. Recovery of chromium of up to 64% was achieved. The addi
tion of methyl chloride to the fuel had a dramatic impact on the speciation
of the chromium emission. The fraction of hexavalent chromium increased si
gnificantly as small amounts of chlorine were added. Partitioning between p
hases was also altered; much more hexavalent chromium was found in the impi
ngers as the chlorine loading increased. Equilibrium calculations reproduce
d experimental trends but showed strong sensitivity to the thermochemical p
roperties of the included species, particularly CrO2Cl2. (C) 2001 by The Co
mbustion Institute.